List Of 100 Best Interview Questions For java Freshers

There is a list of 100 basic Java interview questions. If you have been asked a core Java interview question, please put it in the ask question section. We guarantee that you will find 90% of the frequently requested interview questions and answers here.

The Core Java interview answers are concise and to the point. Basics of Java interview questions, OOPs interview questions, String Handling interview questions, Multithreading interview questions, collection interview questions, JDBC interview questions, and so on.

 

1. What is Java?

   - Java is a high-level, object-oriented, and platform-independent programming language.

 

2. What is the difference between JDK, JRE, and JVM?

   - JDK (Java Development Kit) is a software development kit used to develop Java applications.

   - JRE (Java Runtime Environment) provides the runtime environment for Java applications.

   - JVM (Java Virtual Machine) is an abstract machine that provides the runtime environment in which Java bytecode can be executed.

 

3. Explain the main features of Java.

   - Object-Oriented

   - Platform-Independent

   - Simple

   - Secure

   - Portable

   - Robust

   - Multithreaded

   - Architecture-neutral

   - Interpreted

 

4. What is the difference between `==` and `.equals()` in Java?

   - `==` compares object references.

   - `.equals()` is a method used to compare the content or values of objects.

 

5. What is the `main` method in Java, and why is it important?

   - The `main` method is the entry point for a Java application.

   - It is the method that is called when the program is executed.

 

6. Explain the concept of multithreading in Java.

   - Multithreading is a feature that allows concurrent execution of two or more threads.

   - Threads are lightweight processes within a process.

 

7. What is the `NullPointerException` and how can it be avoided?

   - `NullPointerException` occurs when you try to access an object that is `null`.

   - To avoid it, always check for `null` before accessing an object.

 

8. What is the difference between `ArrayList` and `LinkedList`?

   - `ArrayList` is implemented as a dynamic array, while `LinkedList` is implemented as a doubly-linked list.

   - `ArrayList` provides fast random access, while `LinkedList` provides fast insertion and deletion.

 

9. What is the `finalize` method in Java?

   - The `finalize` method is called by the garbage collector before an object is garbage-collected.

 Best java interview questions 

10. Explain the concept of inheritance in Java.

    - Inheritance is a mechanism in which one class inherits the properties and behaviors of another class.

 

11. What is polymorphism in Java?

    - Polymorphism allows objects of different types to be treated as objects of a common type.

 

12. What is the `super` keyword used for?

    - The `super` keyword is used to refer to the immediate parent class object.

 

13. What is an abstract class?

    - An abstract class is a class that cannot be instantiated and may have abstract methods.

 

14. What is an interface in Java?

    - An interface is a collection of abstract methods. Classes implement interfaces.

 

15. Explain the `final` keyword.

    - The `final` keyword is used to restrict the modification of classes, methods, and variables.

 

16. What is method overloading?

    - Method overloading allows a class to have multiple methods with the same name but different parameters.

 

17. What is method overriding?

    - Method overriding occurs when a subclass provides a specific implementation for a method that is already defined in its superclass.

 

18. Explain the concept of encapsulation.

    - Encapsulation is the bundling of data and methods that operate on the data into a single unit.

 

19. What is a constructor?

    - A constructor is a special method used to initialize objects.

 

20. What is the purpose of the `static` keyword?

    - The `static` keyword is used to create variables and methods that belong to the class rather than instances of the class.

 

21. Explain the `this` keyword.

    - The `this` keyword refers to the current instance of the class.

 

22. What is the difference between `String` and `StringBuffer`?

    - `String` is immutable, while `StringBuffer` is mutable.

 

23. What is the `try-catch` block used for?

    - The `try-catch` block is used to handle exceptions in Java.

 

24. What is the `finally` block used for?

    - The `finally` block is used to execute code, whether an exception is thrown or not.

 

25. What is the purpose of the `throw` keyword?

    - The `throw` keyword is used to explicitly throw an exception.

 

26. What is the purpose of the `throws` clause?

    - The `throws` clause is used to declare the exceptions that a method might throw.

 

27. What is the difference between checked and unchecked exceptions?

    - Checked exceptions must be declared in the method's signature or caught using a `try-catch` block.

    - Unchecked exceptions do not require explicit handling.

 

28. What is the `Collection` framework in Java?

    - The `Collection` framework provides a set of interfaces and classes for managing and manipulating collections of objects.

 

29. What is the difference between an `ArrayList` and a `Vector`?

    - `ArrayList` is not synchronized, while `Vector` is synchronized.

 

30. What is the `Map` interface in Java?

    - The `Map` interface represents a collection of key-value pairs.

 

31. What is the difference between `HashMap` and `HashTable`?

    - `HashMap` is not synchronized, while `HashTable` is synchronized.

 

32. What is the purpose of the `equals` method?

    - The `equals` method is used to compare the content or values of objects.

 

33. Explain the `compareTo` method.

    - The `compareTo` method is used to compare two objects for ordering.

 

34. What is the `instanceof` operator used for?

    - The `instanceof` operator is used to test if an object is an instance of a particular class or interface.

 

35. Explain the concept of garbage collection in Java.

    - Garbage collection is the process of automatically reclaiming the memory occupied by objects that are no longer reachable.

 

36. What is the purpose of the `finalize` method in Java?

    - The `finalize` method is called by the garbage collector before an object is garbage-collected.

 

37. What is the `transient` keyword used for in Java?

    - The `transient` keyword is used to indicate that a variable should not be serialized.

 

38. Explain the `volatile` keyword.

    - The `volatile` keyword is used to indicate that a variable's value may be changed by multiple threads simultaneously.

 

39. What is the difference between `throw` and `throws` in Java?

    - `throw` is used to explicitly throw an exception.

    - `throws` is used to declare the exceptions that a method might throw.

 

40. What is the purpose of the `super()` constructor?

    - The `super()` constructor is used to invoke the constructor of the parent class.

 

41. What is the difference between `finalize()` and `

 

final` in Java?

    - `finalize()` is a method called by the garbage collector before an object is garbage-collected.

    - `final` is a keyword used to restrict the modification of classes, methods, and variables.

 

42. Explain the `instanceof` operator.

    - The `instanceof` operator is used to test if an object is an instance of a particular class or interface.

 

43. What is the purpose of the `break` statement?

    - The `break` statement is used to terminate a loop or switch statement.

 

44. Explain the purpose of the `continue` statement.

    - The `continue` statement is used to skip the rest of the code inside a loop and move to the next iteration.

 

45. What is the `NullPointerException` and how can it be avoided?

    - `NullPointerException` occurs when you try to access an object that is `null`.

    - To avoid it, always check for `null` before accessing an object.

 

46. What is the purpose of the `System.out.println` statement in Java?

    - `System.out.println` is used to print output to the console.

 

47. What is the purpose of the `return` statement in Java?

    - The `return` statement is used to exit a method and return a value to the calling method.

 

48. Explain the difference between `float` and `double` in Java.

    - `float` is a 32-bit IEEE 754 floating-point, and `double` is a 64-bit IEEE 754 floating-point.

 

49. What is the purpose of the `for-each` loop in Java?

    - The `for-each` loop is used to iterate over elements in an array or a collection.

 

50. What is the purpose of the `switch` statement in Java?

    - The `switch` statement is used to select one of many code blocks to be executed.

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